This invention relates to a voice coil support for a coil transducer motor structure and particularly a voice coil support adapted to be placed in a magnetic field in order for the voice coil support to reciprocate along an axis of displacement.
This invention is disclosed in the context of a moving voice-coil transducer motor assembly for a loudspeaker. However, it is believed to be useful in other applications such as microphones, geophones, and shakers.
Generally, voice-coil transducer motor assemblies, such as those used in traditional electrodynamic loudspeakers, comprise magnetic field generating means adapted to generate a magnetic field in which a coil fixed on a moving part also called a mandrel or voice coil support, can be driven by a driving current in order to induce vibrations to a diaphragm connected to the voice coil support to produce sound. In order to improve the yield, as well as to reduce the inertia of the loudspeaker, the voice coil support that is the moving part and the diaphragm that is attached to it, are designed to be as light as possible.
To meet these requirements, the voice coil support is usually a hollow cylinder and the diaphragm a conical piece of material and both are made of a material such as paper, aluminum, polyimide film such as Kapton®, glass fibre or another light composite material.
Reducing the weight of these voice coil supports reduces their rigidity and results in the generation of resonant frequencies. Thus, the frequency response of the voice-coil transducer motor assemblies are affected by nonlinearities.
These nonlinearities occur because of mode coupling between mechanical modes and acoustical modes, resulting in a transfer of energy between mechanical waves and acoustic waves.
This problem leads to some harmonics of the sound produced by the loudspeakers integrating such voice-coil transducer motor assemblies, to be hardly audible and almost extinguished, especially at high frequencies. At lower frequencies, some energy is absorbed during the excitation of the assembly and radiated when the excitation is stopped, leading to longer trailing edges, and the sound produced in the loudspeaker being somewhat unclear.